Actuator having a brushed dc electric motor and an emi reduction circuit

ABSTRACT

An actuator is shown and described. The actuator includes a brushed DC motor and a circuit board. The circuit board for the brushed DC motor includes an EMI reduction circuit and a mounting location for the brushed DC motor. The mounting location includes a resilient conductive member that is surface mounted on the circuit board at the mounting location. When the motor is mounted to the circuit board at the mounting location, the motor case contacts and at least slightly compresses the resilient conductive member, conductively connecting the motor case to the EMI reduction circuit.

BACKGROUND

A brushed direct current (DC) motor operates with a rotating set ofwound wire coils. This rotating set of wound wire coils is oftenreferred to as an armature. The wound wire coils act as an electromagnetwith two poles. Permanent magnets are mounted around the armature suchthat when the poles of the armature pass the poles of the permanentmagnets, they are either pushed or pulled in one direction or another. Acommutator repeatedly reverses the direction of the electric currentprovided to the wound wire coils of the armature such that the poles ofthe armature repeatedly push or pull against the permanent magnets. Thecommutator reverses the polarity of the electric current as the poles ofthe armature pass the poles of the permanent magnets. Inertia keeps themotor moving in the intended direction while the polarity of the polesswitches.

Brushed DC electric motors are often selected for applications where lowcost motors or simple and inexpensive control are required. However,electromagnetic interference (EMI) can be an issue presented by brushedDC motors. Among other reasons for the interference, arcing within themotor case can cause some EMI. It is challenging and difficult toimplement efficient and effective EMI reduction mechanisms.

SUMMARY

One embodiment of the invention relates to a circuit board for a brushedDC motor. The circuit board for the brushed DC motor includes an EMIreduction circuit and a mounting location for the brushed DC motor. Themounting location includes a resilient conductive member that is surfacemounted on the circuit board at the mounting location. When the motor ismounted to the circuit board at the mounting location, the motor casecontacts and at least slightly compresses the resilient conductivemember, connecting the motor case to the EMI reduction circuit.

One embodiment of the invention relates to an actuator. The actuatorincludes a circuit board comprising an EMI reduction circuit. Theactuator further includes a brushed DC motor for mounting on the circuitboard and having a motor case. The actuator yet further includes aspring contact that is surface mounted on the circuit board such thatwhen the motor is mounted to the circuit board, the motor case contactsand compresses the spring contact, conductively connecting the motorcase to an EMI reduction circuit.

The spring contact may be a conductive tab. The conductive tab may be inthe form of a bent strip of conductive material that forms a v-shape.The v-shape includes a first arm, a second arm, and a curved springportion between the first arm and the second arm. The first arm iscoupled to the surface of the circuit board via a solder connection toat least one conductive member that is the part of a conductive path tothe EMI reduction circuit. A surface of the first arm is parallel to thesurface of the circuit board and the second arm extends away from thesurface board and toward the motor casing when the motor is mounted onthe circuit board. The second arm includes an edge, a first portionbetween the curved spring portion and the edge, and a second portionforming the end of the second arm. The second portion forms the end ofthe second arm and includes a loop configured to help prevent the secondarm from being compressed against the first arm.

In other embodiments, the spring contact includes a resilient bodyhaving a conductive member for conductively coupling the motor case tothe EMI reduction circuit. A bottom of the motor case faces the circuitboard. The bottom of the motor case is recessed relative to an outer rimextending about a periphery of the motor case. At least one portion ofthe spring contact extends up into the recess and touches the bottom ofthe motor case when the outer rim is held against a surface of thecircuit board.

The EMI reduction circuit may include at least one capacitorconductively coupled to a ground plane of the circuit board. In many ofthe embodiments disclosed herein, the spring contact is not soldered orotherwise rigidly coupled to the motor case when the EMI reductioncircuit is in use (e.g., conductively coupled to the motor case).

BRIEF DESCRIPTION OF THE FIGURES

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a perspective view of a circuit board for an actuator, inaccordance with an exemplary embodiment.

FIG. 2 is another perspective view of the circuit board of FIG. 1.

FIG. 3 is another perspective view of the circuit board of FIG. 1.

FIG. 4 is an exploded perspective view of a motor and the circuit boardof FIG. 1, in accordance with an exemplary embodiment.

FIG. 5 is a perspective view of a motor coupled to the circuit board ofFIG. 1, in accordance with an exemplary embodiment.

FIG. 6 is a partially broken perspective view of a motor coupled to thecircuit board of FIG. 1, in accordance with an exemplary embodiment.

FIG. 7A is a schematic top view of the circuit board of FIG. 1.

FIG. 7B is a bottom perspective view of the circuit board of FIG. 1.

FIG. 8A is a perspective view of an actuator driven by the motor coupledto the circuit board of FIG. 1, in accordance with an exemplaryembodiment.

FIG. 8B is a cross-section view of the actuator of FIG. 8A.

FIG. 9 is a diagram of an EMI circuit, in accordance with an exemplaryembodiment.

DETAILED DESCRIPTION

Referring generally to the Figures, a circuit board for a brushed DCmotor is shown and described. The circuit board for the brushed DC motorincludes an EMI reduction circuit and a mounting location for thebrushed DC motor. The mounting location includes a resilient conductivemember that is surface mounted on the circuit board at the mountinglocation. When the motor is mounted to the circuit board at the mountinglocation, the motor case contacts and at least slightly compresses theresilient conductive member, connecting the motor case to the EMIreduction circuit.

Some existing actuators having brushed DC motors reduce EMI byreferencing the case or housing to ground or connecting the case to anEMI reduction circuit. Such actuators generally include a grounding wireattachment from the EMI reduction circuit to the case of the motor. Thisgenerally required hand soldering of the connection points between themotor casing and the EMI reduction circuit. Hand soldering a wirecoupled to the motor casing is challenging because the motor case canserve as a large mass heat sink. For this and other reasons, the solderconnection might be unreliable. EMI in actuators having brushed DCmotors has also been reduced by using a common mode choke and capacitorspositioned directly on or across the terminals of the motor forconducting EMI filter. Such circuits can be somewhat effective, but haveissues including low EMI reduction performance relative to the circuitcost.

Referring again to the Figures, a circuit board 10 for an actuator 50(see FIG. 8A) is shown, according to an exemplary embodiment. A motor 36(see FIGS. 4-6, FIG. 8B, and FIG. 9) is coupled to the circuit board 10and to an electromagnetic interference reduction circuit provided on thecircuit board 10. The connection to the EMI reduction circuit is madeautomatically via a spring contact 12 when the motor 36 is coupled tothe circuit board 10.

The spring contact 12 (i.e., resilient member, resilient tab, springtab, etc.) is coupled to the front side of the circuit board 10 in amotor footprint 14. The motor footprint 14 is an area corresponding witha mounting location of the motor 36. The spring contact 12 is coupled tothe EMI circuit provided on the circuit board 10. In one embodiment, theEMI circuit includes one or more capacitors 16 that are referenced toground. One exemplary EMI circuit is illustrated in FIG. 9 as includingtwo capacitors 16, one with a capacitance of 0.1 μF and another with acapacitance of 0.01 μF and each connected to ground. The capacitancevalues of the capacitors utilized in the EMI reduction circuit may bevaried to eliminate unwanted EMI emission peaks at certain frequencies(i.e., a band or bands of frequencies). In varying embodiments, any typeor design of EMI reduction circuit may be closed by the motor casingcoupling with the novel circuit board and spring contact of the presentinvention.

The motor footprint 14 defines an area on the circuit board 10 to whichthe motor 36 may be coupled. As shown, the motor footprint may beprinted on the circuit board to clearly illustrate the proper motormounting location to a user or manufacturer. Within the motor footprint14, the circuit board 10 includes a pair of through-hole contacts 18 forthe motor terminals 38 and two surface mount contacts 20 for the springcontact 12. The circuit board 10 is further shown to include an opening22 (e.g. hole, aperture, bore, etc.) within the motor footprint 14 andconfigured to receive a boss or protrusion 40 extending from the bottomof the motor 36.

The spring contact 12 is a resilient, conductive member that isconfigured to allow the motor 36 to be coupled to the circuit board 10(e.g., with a soldered connection between the terminals 38 and thecontacts 18) and provide a conductive path between the motor 36's casingand the EMI reduction circuit (e.g., the capacitors 16 referenced toground) with no additional assembly steps. The spring contact 12 issized and shaped to apply a slight force to the bottom of the motor 36'scasing that is sufficient to maintain contact between a portion of thespring contact 12 and the motor 36's casing to establish a conductivepath between the motor 36's casing and the spring contact 12, but not somuch force that the spring contact 12 interferes with the proper seatingof the terminals 38 in the through-hole contacts 18 and the motor 36 onthe motor footprint 14 of the circuit board 10.

According to an exemplary embodiment, the spring contact 12 is formed ofa conductive metal such as copper or a copper alloy. In otherembodiments, the spring contact may be another conductive material. Inyet other embodiments, a non-conductive material can form the resilientmember and a conductive material can complete the motor casing-to-EMIreduction circuit connection. For example, the resilient spring membermay have a polymer body and a conductive trace or inlay that extendsfrom the top of the resilient spring member and to a circuit boardcontact for the EMI reduction circuit.

The spring contact 12 is shown in the form of a strip that is bent intoa V-shape with a first arm 24 and second arm with a first portion 28 anda second portion 30 integrally connected at an edge 34. The secondportion 30 is connected to the first arm 24 with a curved spring portion32. The first arm 24 is coupled to the surface contacts 20, such as bysoldering. In an exemplary embodiment, the spring contact 12 is sizedand shaped to function as a cantilever spring with the portions 28 and30 moveable about the curved spring portion 32.

In an exemplary embodiment, the movement of the portions 28 and 30(particularly portion 28) in a downward direction (e.g., toward firstarm 24 and circuit board 10) is limited by the contact of a curved end26 and the top surface of first arm 24. This limit may prevent thecurved spring portion 32 from permanently creasing or otherwise losingits resiliency.

The resilience of the spring contact 12 may be changed by varyingdifferent properties according to varying embodiments. For example, theresilience (i.e., spring constant) may be changed by varying thematerial of the spring contact 12, the cross-section of the stripforming the spring contact 12, and/or the diameter of the spring portion32.

Referring now to FIGS. 4-6, the bottom 46 of the motor 36 is shown to bea recessed structure with an outer rim 44 extending about the peripheryof the motor case or housing 48. A conductive path is formed between themotor case 48, the rim 44 and the bottom 46. A protrusion 40 surroundingan end of the output shaft 42 extends from the bottom 46. The protrusion40 is received in the opening 22 in the motor footprint 14, which allowsthe protrusion 40 to pass through the circuit board 10 and the rim 44 torest on the surface of the circuit board 10. The terminals 38 areblade-like structures extending from the bottom 46 and aligned with thethrough-hole contacts 18. The terminals 38 may be otherwise shaped suchas pin-shaped. In one embodiment, the terminals 38 are providedsymmetrically on either side of the protrusion 40. In other embodiments,the terminals 38 and the contacts 18 may be otherwise arranged, such asto one side of the protrusion 40.

The spring contact 12 is aligned with a portion of the bottom 46 anddoes not obstruct the insertion of the terminals 38 into the contacts 18or the protrusion 40 into the opening 22. The spring contact 12 has aheight that is greater than the height of the rim 44. When the motor 36is fully seated on the motor footprint 14 of the circuit board 10 andthe rim 44 contacts the surface of the circuit board 10, the springcontact 12 is therefore contacted by and compressed by the bottom 46. Inother words, the resilient properties of the spring contact 12 force atleast a portion of the second arm against the surface of the bottom 46to conductively couple the motor case 48 to the EMI reduction circuit.In one embodiment, the edge 34 of the spring contact 12 contacts thebottom 46 of motor casing 48, as shown in FIG. 6. In another embodiment,the first portion 28 or the second portion 30 of the arm may also oralternatively contact the bottom 46 of the casing 48.

Unlike other types of contact, such as a solder ring on the circuitboard 10 or a grounding wire, the spring contact 12 couples the motor 36to the EMI circuit without the need for an additional manufacturing orassembly step. Moreover, the spring contact 12 couples the motor 36 tothe EMI circuit without the need for a rigid mechanical coupling (e.g.,one or more solder points, one or more wires soldered or screwed to thecasing, etc.).

Referring now to FIG. 7B, a pair of test points 52 are provided on thecircuit board 10. The test points 52 are shown as points in the EMIcircuit on both side of the spring contact 12 and each is coupled to oneof the surface mount contacts 20. The test points 52 allow for acontinuity check to be performed to ensure that there is proper contactbetween the spring contact 12 and the bottom 46 of the motor 36. In anexemplary embodiment, the test points 52 may also be used for othertesting or tuning purposes.

While the spring contact 12 is shown as a v-shape, the spring contact 12may be otherwise shaped. For example, the second arm may be curvedinstead of having multiple angles surfaces. In other embodiments, thesecond arm may be coupled to the first arm on either side with a springportion (e.g., in place of a free end 26). In still other embodiments,the spring contact 12 may be a coil spring or a flat washer-shapedspring such as a Belleville washer, spring washer, or wave spring.

While the spring contact 12 is shown as being surface mounted to asurface contact 20, in other embodiments, the spring contact 12 may beinclude an extension or lead that is coupled to a through-hole contact.

While only a single contact 12 is shown in the figures, in anotherembodiment the circuit board 10 may include two or more spring contacts12 disposed in the motor footprint 14 and configured to contact thebottom 46 of the motor 36. For example, a second spring contact may beprovided on the opposite side of the opening 22 from the first springcontact to reduce the torque applied to the connection (e.g., a solderedconnection) between the terminals 38 and the contacts 18. If multiplespring contacts are utilized, the spring contacts may be configured tohave a lower spring constant than that of a single spring contact.Multiple spring contacts may be connected in parallel and each becoupled to the EMI reduction circuit such that contact with any of thespring contacts will couple the case 48 of the motor 36 to the EMIreduction circuit.

FIG. 1 is a front perspective view of the circuit board 10 for theactuator 50, in accordance with an exemplary embodiment. The springcontact 12 is shown disposed in the motor footprint 14 to one side of acentral opening 22. The spring contact 12 is surface mounted to contacts20 on the top face of the circuit board 10.

FIG. 2 is a rear perspective view of the circuit board 10. As shown, thespring contact 12 is coupled to an EMI circuit including a pair ofcapacitors 16.

FIG. 3 is a front right perspective view of the circuit board 10. Whenno motor is coupled to the circuit board 10 in the motor footprint 14,the second arm of the spring contact 12 is biased upward with a spacebetween the first portion 28 of the second arm and the first arm 24coupled to the contact 20.

FIG. 4 is an exploded perspective view of the motor 36 and the circuitboard 10. The pair of leads 38, the central projection 40, and theperipheral outer rim 44 extend from the bottom 46 of the motor 36. Theleads 38 are aligned with the through-hole contacts 18 and theprojection 40 is aligned with the central opening 22. FIG. 5 is aperspective view of the motor 36 coupled to the circuit board 10. Whenthe motor 36 is coupled to the circuit board 10, the outer rim 44 restson top surface of the circuit board 10.

FIG. 6 is a partially broken perspective view of the motor 36 coupled tothe circuit board 10. The spring contact 12 is received in a plenum orchamber below the motor 36 defined by the bottom 46, the outer rim 44,and the top surface of the circuit board 10. The chamber has a heightthat is less than the uncompressed height of the spring contact 12 andthe spring contact 12 is therefore brought into contact with the bottom44 (e.g., along an edge 34).

FIG. 7A is a schematic top view of the circuit board 10 and FIG. 7B is abottom perspective view of the circuit board 10. The surface contacts 20on the top surface of the circuit board 10 are connected to conductivepaths on the bottom surface of the circuit board including the pair oftest points 52. The test points 52 may be used to perform a continuitycheck or for other testing or tuning purposes.

FIG. 8A is a perspective view of the actuator 50 driven by the motor 36and FIG. 8B is a cross-section view of the actuator 50. The motor 36 andthe circuit board 10 are contained within the housing of the actuator 50with the output shaft 42 of the motor 36 engaging the internal mechanismof the actuator 50 (e.g., via a geared connection).

FIG. 9 is a diagram of an exemplary EMI circuit. In one embodiment, theEMI circuit includes two capacitors 16, one with a capacitance of 0.1 μFand another with a capacitance of 0.01 μF and each connected to groundand a spring contact 12 coupled to contacts 20. The motor 36 is coupledto the EMI circuit through the contact between the bottom 44 of themotor 36 and the spring contact 12. The test points 52 are on eitherside of the spring contact 12.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.). For example, the position of elements may bereversed or otherwise varied and the nature or number of discreteelements or positions may be altered or varied. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure. The order or sequence of any process or method stepsmay be varied or re-sequenced according to alternative embodiments.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions and arrangement of the exemplaryembodiments without departing from the scope of the present disclosure.

Although the figures may show a specific order of method steps, theorder of the steps may differ from what is depicted. Also two or moresteps may be performed concurrently or with partial concurrence. Suchvariation will depend on the software and hardware systems chosen and ondesigner choice. All such variations are within the scope of thedisclosure. Likewise, software implementations could be accomplishedwith standard programming techniques with rule based logic and otherlogic to accomplish the various connection steps, processing steps,comparison steps and decision steps. It should be understood that thepresent application is not limited to the details or methodology setforth in the description or illustrated in the figures. It should alsobe understood that the terminology is for the purpose of descriptiononly and should not be regarded as limiting.

What is claimed is:
 1. An actuator, comprising: a circuit board comprising an EMI reduction circuit; a brushed DC motor for mounting on the circuit board and having a motor case; and a spring contact that is surface mounted on the circuit board such that when the motor is mounted to the circuit board, the motor case contacts and compresses the spring contact, connecting the motor case to an EMI reduction circuit.
 2. The actuator of claim 1, wherein the spring contact is a conductive tab.
 3. The actuator of claim 2, wherein the conductive tab is in the form of a bent strip of conductive material that forms a v-shape.
 4. The actuator of claim 3, wherein the v-shape comprises a first arm, a second arm, and a curved spring portion between the first arm and the second arm, wherein the first arm is coupled to the surface of the circuit board via a solder connection to at least one conductive member that is part of a conductive path to the EMI reduction circuit.
 5. The actuator of claim 4, wherein the first arm is substantially parallel to the surface of the circuit board and the second arm extends away from the circuit board and toward the motor casing when the motor is mounted on the circuit board.
 6. The actuator of claim 5, wherein the second arm comprises an edge, a first portion between the curved spring portion and the edge, and a second portion forming the end of the second arm.
 7. The actuator of claim 6, wherein the second portion forming the end of the second arm comprises a loop configured to help prevent the second arm from being compressed against the first arm.
 8. The actuator of claim 1, wherein the spring contact comprises a resilient body having a conductive member for conductively coupling the motor case to the EMI reduction circuit.
 9. The actuator of claim 1, wherein a bottom of the motor case faces the circuit board and wherein the bottom of the motor case is recessed relative to an outer rim extending about a periphery of the motor case; wherein at least one portion of the spring contact extends up into the recess and touches the bottom of the motor case when the outer rim is held against a surface of the circuit board.
 10. The actuator of claim 1, wherein the EMI reduction circuit comprises at least one capacitor conductively coupled to a ground plane of the circuit board.
 11. The actuator of claim 1, wherein the spring contact is not soldered or rigidly coupled to the motor case when the EMI reduction circuit is in use.
 12. The actuator of claim 1, wherein the circuit board comprises a test point exposed at the back of the circuit board that is conductively coupled to the motor casing and the EMI reduction circuit.
 13. The actuator of claim 1, wherein the circuit board contains a graphical outline of a motor footprint and wherein the spring contact surface mounted to the circuit board is located within the graphical outline of the motor footprint.
 14. The actuator of claim 13, wherein the circuit board further comprises at least two through-hole contacts within the motor footprint for receiving motor terminals extending from the motor casing.
 15. A circuit board for an actuator and for direct mounting a brushed DC motor thereon, the circuit board comprising: an EMI reduction circuit comprising at least one tuning capacitor referenced to ground; a portion of the circuit board having a surface for holding one end of casing for the brushed DC motor; a spring contact that is surface mounted on the surface of the portion of the circuit board for holding one end of the casing for the brushed DC motor; wherein the spring contact conductively couples the EMI reduction circuit and the casing for the brushed DC motor when the motor is mounted on the surface and compressing the spring contact.
 16. The circuit board of claim 15, wherein the spring contact is a conductive tab formed by a bent strip of conductive material that forms a v-shape.
 17. The circuit board of claim 16, wherein the v-shape comprises a first arm, a second arm, and a curved spring portion between the first arm and the second arm, wherein the first arm is coupled to the surface of the circuit board via a solder connection to at least one conductive member that is part of a conductive path to the EMI reduction circuit.
 18. The circuit board of claim 17, wherein the first arm is substantially parallel to the surface of the circuit board and the second arm extends away from the circuit board and toward the motor casing when the motor is mounted on the surface of the circuit board.
 19. The circuit board of claim 18, wherein the second arm comprises an edge, a first portion between the curved spring portion and the edge, and a second portion forming the end of the second arm.
 20. The circuit board of claim 19, wherein the second portion forming the end of the second arm comprises a loop configured to help prevent the second arm from being compressed against the first arm. 